With continuous development of large-scale integrated circuits, an integration level of integrated circuits is continuously increased and a feature size of MOSFETs is decreased beyond the 22 nm node. Actually, it becomes more and more difficult to fulfill the requirement of Moor law after the 90 nm node by simply reducing a gate length. When the gate length is reduced, heavily doping is performed in a channel region for suppressing short channel effects, which, however, causes scattering due to the channel doping and a strong field effect and increased parasitic resistance. Consequently, mobility of carriers in the channel region is decreased, which impairs improvement of electrical performances of the device. In view of this, stress engineering is proposed as a important approach to increasing mobility of carriers in the channel region.
Such an approach utilizes various sources of stress to apply stress to the channel region in the manufacture of the device, such as strained overlayers, stress memorization, and embedded SiGe (eSiGe). The stress, if being appropriately applied, will increase mobility of carriers in the channel region and improve electrical performances of the device even in a case that a size of the channel region is continuously reduced.
A metal gate is widely used in a CMOS device after the 45 nm node. As an extension of SMT technique, an approach of introducing the stress to the channel region by the metal gate is proposed as required, especially for an NMOS device. Thus, it is a necessary task to study the NMOS device with TiNx as a material of the metal gate and to study its stress effect.
Conventional methods for forming a TiN film, such as evaporation, (magnetron) sputtering, PECVD, etc., may obtain a TiNx film with 1 to 2 GPa stress by controlling process parameters. However, with continuous reduction of the device size, a demand on increasing carrier mobility in the channel region is increased. It is difficult for the conventional methods for forming the TiNx film as described above to fulfill the requirement for increasing driving capability of the device by varying process parameters.